The ornamental design for a mirror, as shown and described.
FIG. 1 is a perspective view of the mirror in accordance with a first embodiment of the present invention.
FIG. 2 is a front elevational view of the mirror of FIG. 1.
FIG. 3 is a rear elevational view of the mirror of FIG. 1; and,
FIG. 4 is a left side elevational view of the mirror of FIG. 1, the right side, top and bottom elevational views being a mirror reflection of the left side elevational view.